Reinforcing bars for use in reinforced concrete are well known. Such rods are placed within reinforced concrete, such as pre-stressed concrete, to enhance the strength of a structure.
Frequently, such bars have ribs extending from their circumferences to improve the adhesion of the bars within the surrounding concrete. Deformed bars have one or more series of parallel transverse ribs that extend around the circumference of the bar. In addition, the bars may have longitudinal ribs, which are formed during the manufacturing process. The transverse ribs may extend perpendicularly between the longitudinal ribs. Alternatively, the transverse ribs may be set in an inclined manner so as to extend at a non-perpendicular angle from the longitudinal ribs.
Prior art, including prior art reinforcing bars, is disclosed in the following documents: U.S. Pat. No. 3,561,185 (Finsterwalder), U.S. Pat. No. 4,033,502 (Rothchild), U.S. Pat. No. 4,056,911 (Tani), U.S. Pat. No. 4,076,163 (Grande), U.S. Pat. No. 4,092,814 (Kern), U.S. Pat. No. 4,114,344 (Heasman), U.S. Pat. No. 4,143,986 (Antosh), U.S. Pat. No. 4,193,686 (Kern), U.S. Pat. No. 4,229,501 (Kern), U.S. Pat. No. 4,241,490 (Edwards), U.S. Pat. No. 4,469,464 (Andrews), U.S. Pat. No. 4,584,247 (Mulholland), U.S. Pat. No. 4,619,096 (Lancelot III), U.S. Pat. No. 4,627,212 (Yee), U.S. Pat. No. 4,666,326 (Hope), U.S. Pat. No. 4,811,541 (Finsterwalder), U.S. Pat. No. 4,922,681 (Russwurm), U.S. Pat. No. 5,046,878 (Young), U.S. Pat. No. 5,067,844 (Bowmer), U.S. Pat. No. 5,152,118 (Lancelot), U.S. Pat. No. 5,158,527 (Bernard), U.S. Pat. No. 5,411,347 (Bowmer), U.S. Pat. No. 5,468,524 (Albribo), U.S. Pat. No. 5,664,902 (Holdsworth) and U.S. Pat. No. 5,669,196 (Dahl).
Reinforcing bars are frequently connected to one another to permit the transfer of force between them. Thus short reinforcing bars can be used in larger concrete structures. One method of connecting such bars is to ensure that they are positioned so as to overlap such that there is force transfer from one bar to another through the concrete surrounding them. A further example of connecting reinforcing bars is to weld them directly together. In this instance, the distance between the bars is shorter and the bars transfer force directly through the weld.
A third method of connecting reinforcing bars end to end is to use a mechanical connecting means. Some of these mechanical connecting means, or internally threaded members, rely upon threads for attachment to the reinforcing bars. Standard threads may be cut into a portion of the circumference of the reinforcing bar after the transverse ribs are removed along that portion. Cutting threads into a reinforcing bar may be both expensive and time-consuming.
Alternatively, a coupler having internal threads may attach to the inclined transverse ribs of a reinforcing bar. In this instance, the longitudinal ribs must be absent from the reinforcing bar so that the path of the internally threaded member upon the inclined transverse ribs is not obstructed. Furthermore, the dimensions of the transverse ribs must be precise and consistent to ensure that the coupler holds the reinforcing bars together tightly to permit for the efficient transfer of force between them. Attaching the coupler to the reinforcing bars is particularly challenging when the transverse ribs do not form a continuous spiral as in U.S. Pat. No. 4,229,501 (Kern) and U.S. Pat. No. 4,584,247 (Mulholland).
Ordinary deformed reinforcing bars are manufactured in steel rolling mills by a hot rolled production process. During this process, a billet having a square cross-section, which has been warmed in a reheating furnace, is fed through sets of opposed rollers. After the billet has been shaped into a bar, it is finished by adding both the transverse ribs and longitudinal ribs. The longitudinal ribs represent excess steel formed during the rolling process due to inconsistencies in the circumference of the deformed reinforcing bar along its length. The finished bar is then cut to a pre-determined length.
Alternatively, the threaded reinforcing bar may be manufactured without longitudinal ribs. During this process, the circumference of the reinforcing bar must be constant along its length, such that no longitudinal ribs are formed. The resulting reinforcing bar will have series of transverse ribs. Such transverse ribs form an interrupted spiral upon which a coupler may engage. An interrupted spiral prevents the smooth engagement of the coupler upon the threaded reinforcing bar. To obtain a continuous spiral transverse rib, an expensive and time-consuming process other than the hot rolling process is necessary. Specifically, a manufacturer cannot rely upon longitudinal ribs to account for inconsistencies along the length of the reinforcing bar while forming the continuous spiral rib, thus necessitating a more precise and time-consuming manufacturing process. Such a threaded reinforcing bar is more expensive to produce than a deformed reinforced bar formed with longitudinal ribs because of the precise method of manufacture that is necessary.
It is thus an object of the present invention to provide an improved reinforcing bar and a method of manufacturing such a bar.